Brake Problem with my Car

[Bad340fish]

Just wanted to ask some gurus about this.



On my Barracuda I have a Wilwood Disc Brake setup on the front and the stock 10x2. 5" drums on the back. The wilwoods only have about 50 miles on them if that much. Car stops great! It has a very good pedal also. BUT when I go to Stall the car up on the line I lose the pedal and the car drives off. I can hammer down on the pedal with the car sitting still and it will hold. But when I hammer down on the pedal and Apply the gas to stall up it just goes away. The car does not have power brakes.



The only thing I have done sofar is to try bleeding them again which did not help any. But I am going to race this weekend and have got to figure this problem out. Could the Master Cylinder be to small for the new brakes? Just wanted to get some ideas before I go to wrench on it. TIA



BTW The brake fade was reduced by at least %75 over the stock 10" drums. The Wilwoods for the rear are Next!

Clark

 

[Hammer]

Racing brakes 101

Fish,,This could be one or more problems in the braking system,First thing you should do is eliminate the obvious,,Check ALL brake line front to rear and inspect for any signs of leaks,Next pull the rear drums and look to see if you have rear wheel cylinders leaking (notorious for giving the spongy pedal feel after a brake job,I myself during a reline session on my cars will either rebuild them or replace them,after all you do want to stop at speed why chance it),,I also use a performance brake fluid to withstand higher heat that is produced during the burnout and high pressure stops at those annoying short tracks,,Pull the master cylinder and see if it is leaking from the rear where you can not visually see it,,Replace the brake portioning valve and see if that also helps(it will also cause the spongy feel and pressure loss,,I have run the wildwood brakes and stock drums in my pro-street unit for years with no problems on a stock master cylinder,providing it is not leaking,,One last thing,with the high speed stops needed,I always pressure bleeded my braking system making sure all the air was removed,,One last thing,racers 101 now,,I'm not sure how hard you stall the convertor,but,get someone to video the car during the staging process and leave to see if you may be pushing thru by being up on the convertor to hard,after all,when the missle is ready to go all your doing is stressing a braking system you'll need at the big end to stop a 3200 to 3500 lb projectile and at big mph,,Let me know how you make out,,If you need a hand let me know... .

 

[Bad340fish]

Hammer, I changed gears on saturday so I had the drums off and did not see any leakage at the wheel cylinders. I am pretty sure its not pushing the front tires because its losing the pedal when i stall. I do not stall it that hard really. I have a Turbo Action 8" Converter that I normally only push to 3000. With my Drums I could get 4200 from that converter with some effort. Thanks for the reply. I am going to go work on the thing some tonight

Clark

 

[B.G. Smith]

If you are losing the pedal while staging and there are no external leaks, the master cylinder is leaking internally ( fluid is by-passing the piston). To confirm, try this, with the engine off, press the break pedal hard then ease off slightly but don't release, re-apply, repeat several times, if it is the master cylinder, the pedal will gradually go to the floor. bg